DE202021003680U1 - Crucible for cathode materials - Google Patents

Abstract

Crucible, in particular for at least one cathode material, comprising an oxidic fiber composite material, the fiber composite material containing oxidic ceramic fibers which are introduced into a matrix, the matrix containing at least one metal oxide.

Description

The present invention relates to a crucible, in particular for cathode material or cathode materials, comprising an oxidic fiber composite material, the fiber composite material containing oxidic ceramic fibers which are introduced into a matrix, the matrix containing at least one metal oxide.

With the move away from fossil fuels, the storage of electrical energy is increasingly becoming the focus of everyday life, with electrical energy usually being stored in batteries. Batteries are divided into primary and secondary energy storage. While chemical energy is irreversibly converted into electrical energy in primary energy storage, secondary energy storage (accumulators) enable multiple uses due to the possibility of reversing a chemical reaction that has taken place by supplying electrical energy, so that the latter is preferred, especially for most technical applications. For example, secondary energy stores with an active cathode material based on lithium ions are used in a wide variety of fields of application. Examples include cell phones, portable computers, and especially electric and hybrid vehicles.

Due to the widespread use of lithium-ion batteries, active cathode materials are required in large quantities and with a strong upward trend. It is currently customary to use lithium mixed metal oxides with the transition metals nickel (Ni), manganese (Mn) and/or cobalt (Co) as the active cathode material. The most commonly produced cathode materials are lithium _{nickel cobalt manganese oxide (Li a} Ni _x CO _y Mn _z O ₂ , x + y + z = 1, a usually ≥1) and lithium cobalt oxide (LiCoO ₂ ), and lithium nickel cobalt aluminum oxide (especially LiNi _x Co _y Al _z O ₂ , x + y + z = 1) and lithium iron phosphate (LiFePO ₄ ).

In the large-scale production of cathode materials, the respective starting materials are usually transported through a conveyor (roller oven) in a crucible, also known as a "square capsule or V-capsule" because of its shape, and heated to a temperature of several hundred degrees Celsius chemical conversion to the desired product takes place.

It has been shown in practice that the "V-caps" are subject to considerable corrosion. The reason for this is the chemical aggressiveness of the substances transported in the V-capsule, which strongly attack the material of the V-capsule at the high temperatures in the oven. Particularly in the production of Li _a Ni _x Co _y Mn _z O ₂ , the capsules corrode very severely because of the particularly aggressive transition metals. The disadvantage of this is that the capsules only allow a relatively small number of uses and have to be replaced quickly. Usually the capsules can only be used for 20-40 production cycles. To make matters worse, the capsules can contain residues of the cathode powder after use, which necessitates complex and expensive disposal. In addition, capsule materials can contaminate the cathode powder, leading to its contamination and overall reduced quality.

State of the art:

Currently, when heating the cathode powder described, V-capsules made from spinel-cordierite-mullite mixtures are used, usually with an Al ₂ O ₃ content of 50-70% by weight, an SiO ₂ content of 10-25% by weight, and an MgO content of 15-30% by weight, the % by weight adding up to 100% by weight. These materials withstand well the temperature gradients of 200-500° C./h that occur during the production firing of the cathode powders described. However, these "furnace materials" corrode severely and thus achieve a very limited life cycle with high contamination of the cathode powder.

However, there is still the problem of providing a crucible, in particular for cathode material or cathode materials, which can be used for longer and leads to less corrosion.

The inventors found a crucible that solves the problems of the prior art. In particular, a crucible according to the invention has good thermal shock resistance of the monolithic aluminum oxide with significantly improved corrosion properties at the same time. A further advantage results from the achievable thin walls of the crucible and thus a significant saving in weight, with the strength level of the crucible also being able to be significantly increased compared to those of the prior art. The thin walls of the crucible also allow a significantly improved (faster) energy absorption of the cathode powder and thus energy savings.

The present invention relates to a crucible, in particular for at least one cathode material, comprising an oxidic fiber composite material, the fiber composite material containing oxidic ceramic fibers which are introduced into a matrix, the matrix containing at least one metal oxide. A crucible according to the invention can be commonly used for a specific cathode material, but is not limited to use for a specific cathode material, and a crucible of the present invention can be used for a variety of cathode materials.

Further aspects of the present invention can be found in the dependent claims and the detailed description.

Description of the figures

The accompanying drawings are intended to illustrate and provide a further understanding of embodiments of the present invention. In the context of the description, they serve to explain the concepts and principles of the invention. Other embodiments and many of the foregoing advantages will become apparent by reference to the drawings. The elements of the drawings are not necessarily drawn to scale with respect to one another. Identical, functionally identical and identically acting elements, features and components are provided with the same reference symbols in the figures of the drawings, unless otherwise stated.

1 shows schematically a cross section of a crucible 1 according to the invention.

Detailed description of the invention

definitions

Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art of the invention.

Quantities in the context of the present invention relate to % by weight, unless stated otherwise or is apparent from the context.

A crucible is a fireproof and preferably chemically resistant vessel for heating substances and/or producing melts. Within the scope of the present disclosure, the crucible is not particularly restricted in terms of shape, dimensions and design, provided that it can be used to hold a material to be melted, in particular a cathode material, more particularly a cathode material for lithium batteries. In particular for the processing of cathode material, a crucible can be designed, for example, as an open cuboid with an open rectangular cross section, as for a crucible 1 in 1 shown schematically and not to scale.

In the crucible of the present invention, the oxide fiber composite material is not particularly limited, as are the oxide ceramic fibers and the matrix containing at least one metal oxide. The fiber composite material is characterized in that the fibers are introduced into the matrix, for example in the form of a scrim, a knitted fabric or a braid. According to certain embodiments, the fibers are randomly introduced into the matrix, such as can be achieved with fiber spraying. In this way, a surface-isotropic profile of properties can be achieved, which is advantageous for crucibles.

According to certain embodiments, the oxide ceramic fibers are aluminum oxide and/or mullite-based fibers, aluminum oxide fibers being preferred. Although it is not excluded that different oxidic ceramic fibers are present in a crucible according to the invention, it is preferred according to certain embodiments if only one type of oxidic ceramic fiber is present. Good formability and good adhesion of the matrix during production can be achieved in particular with fibers made of aluminum oxide and/or mullite, so that crucibles with good dimensional stability and strength are obtained.

According to certain embodiments, the oxidic ceramic fibers are fibers with a length of 1 mm to 150 mm, preferably 2 to 115 mm, more preferably 3 to 100 mm, which are preferably cut, ie in particular short fibers with a corresponding length. The manner of cutting is not particularly limited. However, the oxidic ceramic fibers preferably have an essentially homogeneous distribution in terms of length in order to achieve uniform strength in the final crucible. Sufficient strength of the crucible is achieved in particular with fibers of such a length. The fibers can be introduced into the matrix individually and/or as a bundle. According to certain embodiments, the fibers are introduced into the matrix as bundles, for example randomly. For this purpose, the fibers can also be cut during insertion. When fiber bundles are used, the number of fibers in the bundle is not particularly limited, and a bundle may comprise, for example, 100 to 50000 individual fibers, for example 500 to 10000 individual fibers, eg 1000 to 5000 individual fibers. Suitable fibers or fiber bundles and/or fabrics are, for example, Nextel™ 610 (Al ₂ O ₃ ) or Nextel ⁷²⁰ (based on mullite) from 3M™ (available as fibers on a roll (rovings) as well as woven fibers, which can be cut to a suitable length if necessary.

In particular in a fiber spraying process, fiber bundles can be introduced in such a way that the bundle structure is retained in the matrix and it does not disintegrate into individual fibers. However, it cannot be ruled out that the fibers are also partially or completely present as individual fibers in the matrix, as can happen, for example, when fibers are dispersed and/or homogenized in a slurry, that fiber bundles are separated, and/or it can also targeted individual fibers are introduced.

According to certain embodiments, a large number of oxidic ceramic fibers are present in a crucible according to the invention, for example as fiber fabric and/or as sections of fiber bundles, which are introduced into a matrix, the matrix containing at least one metal oxide. The type of fiber fabric and/or the fiber bundle is not particularly restricted here, nor is its introduction into the matrix. For example, the fibers, fiber bundles and/or the fiber web can be introduced into a matrix in the form of a slip, which can then be suitably dried. It is also possible to spray fibers, for example also in the form of fiber bundles, and slip onto a shaped body at the same time. Layers produced with such a spraying process can then also be assembled into plates, from which a crucible can then be formed.

Auxiliaries such as dispersing aids and/or solvents such as water and/or glycerol can also be added to the matrix for slip production, but these are preferably expelled again when the crucible is produced. Although it cannot be ruled out that traces of dispersing aids, solvents or the like may still be found in a crucible according to the invention, it is preferred that these are expelled during production of the crucible, for example in a drying and/or sintering step .

According to certain embodiments, the matrix comprises aluminum oxide and optionally zirconium dioxide (ZrO ₂ , zirconium oxide). According to certain embodiments, the matrix comprises alumina and zirconia. Although it cannot be ruled out that further additives are present in the matrix, which are not particularly restricted, according to certain embodiments the matrix consists of aluminum oxide and possibly zirconium dioxide, ie consists for example only of aluminum oxide, or consists of aluminum oxide and zirconium dioxide. If the matrix consists of aluminum oxide and zirconium oxide, the proportions thereof are not particularly limited, the matrix containing, for example, 40 to 90% by weight aluminum oxide and 60 to 10% by weight zirconium oxide, for example 60 to 85% by weight aluminum oxide and 40 to 15% by weight % zirconia, eg 70 to 80% by weight alumina and 30 to 20% by weight zirconia, eg about 75% by weight alumina and about 25% by weight zirconia. Aluminum oxide and zirconium dioxide in particular are particularly suitable for the production of a crucible according to the invention, since these can be sintered at temperatures at which the resistance of the preferred oxidic ceramic fibers is not impaired, for example at a maximum of 1250.degree. It also follows from this that other materials can also be present in the matrix, which enable a corresponding sintering temperature. The matrix is then no longer particularly restricted with regard to the final shape and can also be porous, for example.

The matrix can be physically connected to the fibers by sintering. According to certain embodiments, there is at least one physical bond between fibers and matrix in a crucible according to the invention. The type of bonding can result in porosity in the final crucible material. According to certain embodiments, a crucible according to the invention has a porosity of 17 to 43%, preferably 20 to 40%, which results, for example, when fiber fabrics are used. In this case, the porosity can be suitably determined, for example, by a buoyancy measurement or by a hydrostatic method. For example, the crucible can also be soaked with water for this purpose, in which case the measurement can then be carried out, e.g. by boiling, drawing a vacuum, etc., to separate the water. When using short fibers, however, a porosity of 30 to 42%, preferably 35 to 40%, can also be achieved, for example.

According to certain embodiments, the crucible is a square capsule. With these capsules, also called V-capsule, a further optimization of the crucible in terms of capacity is possible. Especially for the processing of cathode materials, the use of square capsules is advantageous because they can be stored side by side with high efficiency, while at the same time ensuring good stability of the crucible and the cathode material can be processed effectively. In this regard, a square capsule can also be seen as a kind of transport trough suitable for transporting and heating chemical substances, especially as a transport trough in the manufacture of cathode materials for lithium-ion batteries.

According to certain embodiments, the wall thickness of the crucible is between 0.5 and 7 mm, preferably 1 to 5 mm, for example 2 to 3 mm. It cannot be ruled out here that the thickness of a bottom of the crucible differs from the thickness of a wall, for example by more matrix fiber layers being provided in the bottom area during manufacture. However, according to certain embodiments, the thicknesses of the walls and bottom of the crucible are substantially the same. Surprisingly, it has been shown that the combination of oxidic ceramics with the matrix also makes it possible to achieve thinner walls with sufficient strength compared to the prior art.

According to certain embodiments, the crucible consists of one or more layers of a fabric made of the oxidic ceramic fibers which are connected to the matrix. The strength can be further increased by using layers, since this also enables alignment and better distribution of the fibers. The number of layers is not particularly limited here and depends, for example, on the wall thickness to be achieved, but can also depend on the fiber type, for example. Although it is not excluded that crucibles according to the invention make do with one layer, the crucible can have more layers, e.g. with a wall thickness of 5 mm depending on the fiber 5 to 20 layers, e.g. 9 or 17 layers. Accordingly, according to certain embodiments, a crucible may consist of 1 to 25, e.g., 1 to 20 layers.

According to certain embodiments, individual layers have been produced by a fiber spraying process, such as that described in EP 3450128 A is described. The fiber spraying process is not particularly limited here. For example, a slip can be sprayed onto a plurality of fibers and/or a fibrous web, or the fibers and the slip can be sprayed together, for example onto a suitable substrate. The spraying process not only enables simple shaping, but also good dimensional stability and the achievement of a uniform thickness, since a corresponding control is possible as a result. After the spraying process, the crucible can then also be produced simply by conditioning, possibly cutting and/or stacking and possibly laminating and pressing, drying and sintering, with the shaping of the crucible being able to be carried out at a suitable point, for example before, during or after the drying. The method is not particularly limited in this regard.

According to certain embodiments, the crucible has a rectangular shape with a length and/or a width ranging from 100 to 500 mm and/or a height ranging from 50 to 200 mm. In particular, a crucible according to the invention has a length and width of 330 mm and a height of 100 to 150 mm. This makes it possible to arrange a large number of crucibles next to one another, for example for melting cathode material.

According to certain embodiments, the crucible has a weight of 0.5 to 3.0 kg. Compared to conventional crucibles, a weight saving can be achieved with the present crucibles, which can have an advantageous effect on the wear of plant parts, such as conveyor belts, etc., during use.

The above embodiments, refinements and developments can be combined with one another as desired, insofar as this makes sense. Further possible refinements, developments and implementations of the invention also include combinations of features of the invention described above or below with regard to the exemplary embodiments that are not explicitly mentioned. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

The invention will be explained in further detail below with reference to various examples thereof. However, the invention is not limited to these examples.

Comparative example 1

Typical commercially available spinel-cordierite-mullite V-caps measuring 330 x 330 x 100 mm have a wall thickness of 10-12 mm to give sufficient strength and weigh 7-8 kg. The density is about 2.6 g/cm ³ .

Comparative example 2

In order to achieve a further weight reduction, a V-cap according to the dimensions of Comparative Example 1 was produced with Al ₂ O ₃ . This showed significantly less corrosion compared to Comparative Example 1. However, the poor thermal shock resistance of commercially available Al ₂ O ₃ materials prevents use as V-capsules of the specified size when firing cathode powders.

example

In order to be able to compensate for the disadvantages of monolithic aluminum oxide, it was considered to provide the material with fiber reinforcement.

For this purpose, a mixture, produced by soaking bundles of short aluminum oxide fibers with a length of about 14 mm with a slip comprising an aluminum oxide/zirconium dioxide mixture (75/25% by weight and a dispersing agent in water and glycerol, sprayed into individual layers of fabric. Alternatively, it is also possible to spray a corresponding slip onto a fabric made from the fibers.

The fiber spraying process creates layers which, depending on the thickness, are then pressed together, if necessary pre-dried (in particular to remove at least part of the water), formed into a crucible and then sintered for a short time at 1250 °C to remove water, glycerol and to remove the dispersing agent.

A special form of production is the use of cut individual fiber bundles (short fiber bundles). The spraying process makes it possible to spray cut short fiber bundles and/or short fibers and slip onto a shaped body at the same time. Alternatively, it is also possible to create a plate in this way and to shape it.

At a thickness of 2.5 mm and a typical density of 2.4 g / cm ³ (in case of short fibers, in tissue can also be higher, for example at 2.6 g / cm ³ may be), the weight of a capsule of the same size at 1 .5 (1.6) kg and thus weight savings by a factor of 5.

The problem of the poor thermal shock resistance of the monolithic aluminum oxide is solved with a V-capsule produced according to the example, with improved corrosion properties at the same time. A further advantage results from the thin walls of the V-capsule, which can be achieved and thus a significant saving in weight. In addition, the strength level of the V-capsules can be significantly increased.

By using OCMC (Oxide Ceramic Matrix Composite) materials, it is possible to reduce the wall thickness from 10-12 mm to 2-3 mm compared to conventional V-capsules. With the same density, this results in a high weight saving. This is another advantage in addition to the improved corrosion behavior. The thinner wall thickness also results in a higher capacity.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 3450128 A [0027]

Claims (10)

Crucible, in particular for at least one cathode material, comprising an oxidic fiber composite material, the fiber composite material containing oxidic ceramic fibers which are introduced into a matrix, the matrix containing at least one metal oxide. crucible after claim 1 , the oxidic ceramic fibers being aluminum oxide and/or mullite-based fibers. crucible after claim 1 or 2 , wherein the matrix comprises alumina and optionally zirconia. Crucible after one of Claims 1 until 3 wherein the crucible is a square capsule. Crucible after one of Claims 1 until 4 , wherein a wall thickness of the crucible is in a range from 1 mm to 5 mm. Crucible after one of Claims 1 until 5 , wherein the crucible consists of one or more layers of a fabric made of the oxidic ceramic fibers, which are connected to the matrix. crucible after claim 6 , where individual layers were produced by a fiber spraying process. Crucible after one of Claims 1 until 7 , wherein the oxide ceramic fibers are fibers with a length of 1 mm to 150 mm, which are preferably cut. Crucible after one of Claims 1 until 8th , wherein the crucible has a rectangular shape with a length and/or a width in the range of 100 to 500 mm and/or a height in the range of 50 to 200 mm. Crucible after one of Claims 1 until 9 , the crucible having a weight of 0.5 to 3.0 kg.

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